Methods to detect and identify microorganisms are typically conducted on separate automated systems in clinical laboratory and industrial settings. Standard automated blood culture instruments are restricted to a detection system that gives either a positive or negative result but does not provide any information about the characterization or identity of the microorganism. Aside from testing with molecular based assays, which are expensive and generally limited to specific microorganisms, the identity of the microorganism is typically established by taking a sample from a positive blood culture bottle and conducting a separate identification test, usually after an overnight subculture step to prepare the organisms for identification testing.
WO2007/019462 generally relates to a method for the identification and quantification of a biological sample based on measurement of a fluorescence Excitation-Emission Matrix (EEM) at a single time point. The sensitivity of this approach is limited because the quenching, fluorescence, and reflectance properties of the surrounding medium within which the biological sample of interest is contained can interfere with the measurement. If the microorganism is in a homogeneous and transparent sample, such as water or saline, the system is operable. However, for turbid, optically dense, or other complex samples, such as blood, the system is inefficient because the variability of the complex background complicates the microorganism spectrum when measured at only a single time point. Small changes in reflectance and fluorescence of the microorganism cannot be measured with a single EEM reading because the variability in background signals of turbid samples is greater than the specific signal emitted by the microorganism. Thus, sensitive detection and early characterization or identification of the biological entity in a complex sample is generally not practical with a single measurement approach as taught by this reference.
There is a continued need for automated systems to provide additional capabilities in monitoring, detecting and/or characterizing biological particles, particularly microorganisms. Alternative methods for earlier detection and characterization are also desirable because there is a benefit in clinical settings to provide early results to physicians as more appropriate therapy can be selected at or around the time the blood or sterile body fluid culture is shown as positive for microbial growth. Additional information in a shortened timeframe would also be helpful for non-clinical uses of the system as well.